Knitted fabric of steel fibers with increased number of stitches

ABSTRACT

A knitted fabric comprises fibers. At least part of these are metal fibers. The fabric has 90 or more stitches per square centimeter. The fabric is used as a separation cloth ( 12 ) between mould ( 11 ) and glass ( 14 ). The increased number of stitchers per square centimeter reduces the risks for markings on the glass.

FIELD OF THE INVENTION

The invention relates to a knitted fabric comprising fibres (fibers), atleast part of these fibres being metal fibres and the use of such fabricas a separation cloth for moulds in glass bending processes.

BACKGROUND OF THE INVENTION

Such knitted fabrics comprising metal fibres are described in thePCT-patent applications WO97/04152, WO94/01372 and WO94/01373 and areutilised in various fields of application.

The use of a textile fabric as separation cloth between mould and glass,to form side-lites and back-lites for automotive business is known.During this contact, temperatures of 650 to 700° C. are used. It is ofgreat importance that no marks are left on the glass surface after thecontact of the glass and the textile fabric.

The use of textile fabrics out of 100% glass fibres is known. Thedisadvantage of these glass fibre cloths is that it doesn't resist themechanical action during the glass shaping process. Also the use oftextile fabrics, partially or fully consisting out of metal fibres isknown. Using these fabrics as mould coverings, the mechanical action ofthe bending process is withstand better, but there is still the risk ofmarking the glass, by transferring the woven or knitted pattern into theglass surface which has contacted the textile fabric.

Further, it is known that the use of knitted structures is more suitableto cover moulds, since knitted surfaces can be draped better on mouldsand less or no folds will be created when bending the knitted fabric,especially on three-dimensionally shaped surfaces or moulds.

The risk of having marks, caused by use of textile fabrics as theseparation cloth for moulds in glass bending processes, is influenced byseveral parameters, such as glass temperature and pressure used to bendthe glass. Since for example the automotive industry requires morecomplex glass surfaces, that is glasses which show a deeper bend, theglass has to be heated to a higher temperature and the pressure to bendthe glass, is increased as well. These two adjustments to the productionparameters of the bending process, makes the glass more sensitive tomarkings since higher temperature makes the glass softer, and creates amore obvious transfer of the textile structure, either woven or knitted,on the glass surface because of the higher pressure.

Another parameter that influences the risk of marking, is the wear ofthe textile fabric, used as a separation cloth between moulds and glass,due to the repetitive contacts with glass sheets, and the temperature.This temperature makes the fibres become more sensitive to breakingforces, and the mechanical action of the glass sheets against the fabricmakes the fabric wear out little by little. Since the fibres which arestanding out on the yarn surface, will suffer most on this mechanicalaction, and so will disappear after several contacts with glass, thestitches out of which the knitted fabric is made or the weaving pattern,used to provide the woven fabric, will be transferred more obviously tothe glass surface.

Separation cloths should preferably meet next requirements:

1. The cloth should resist the bending temperature. Typically, thesetemperatures raise up to 700° C. when the bending takes place in theheated part of the furnace. When the glass bending takes place out ofthe furnace, this temperature will be less.

2. The cloth should be able to follow the mould shape as close aspossible.

3. The separation material should show enough air permeability. It istaken as a limit that separation cloths should at least have an airpermeability of 2400 l/10 cm^(2*)h, and preferably more than 4500 l/10cm^(2*)h.

4. The weight of the separation cloth is preferably between 600 g/m² and2000 g/m². Fabrics with less weight usually wear out too fast, where tooheavy fabrics tend to elongate too much under its own weight, so causingobstruction in the furnace for the glasses to pass in the neighbourhoodof the fabric before or after the bending action.

5. The thickness for the separation cloth is preferably more than 0.8 mmand even better more than 1 mm. Too thin fabrics show a lack ofelasticity in the direction perpendicular to the fabric surface.

6. And as already mentioned, the risk for remaining marks on the glasssurface should be reduced to a minimum.

The higher the number of requirements met, the better the performance ofthe separation cloth between mould and glass in the glass bendingprocess will be.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a fabric with areduced risk for markings on the glass surface.

It is also an object of the present invention to provide a fabric whichmeets all of the above-mentioned minimum requirements.

The invention relates to a knitted fabric, which comprises fibres, atleast part of these fibres being metal fibres, and which has more than90 stitches per square centimetre.

Preferably the knitted fabric has more than 95, most preferably morethan 100, e.g. more than 105 or even more than 110 stitches per squarecentimetre.

The first requirement, being the resistance to the temperatures used forthe bending of the glass, is met by the use of metal fibres, usuallystainless steel fibres.

Possibly, other high temperature fibres, such as glass fibres, ceramicfibres, TWARON®, NOMEX®, meta-aramid fibres, para-aramid fibres, carbonfibres, preox-fibres and other high temperature resistant man-madefibres can be used, next to the metal fibres. The fibres, of which atleast one are metal fibres, can be intimately blended and possibly pliedto a two or more plied yarn or the yarn can be a two- or more pliedyarn, where some or all of the single yarns are made out of one fibretype.

By plying yarns, it is meant that two or more yarns are given a torsionround the direction of the axis's of the yarns.

To meet the second requirement, being the drapeability, usually knittedstructures are used.

The other characteristics, air permeability, thickness, weight andnumber of stitches, are largely influenced by the gauge of the knittingmachine, the metrical number of the used yarns, the knitting structureand the settings of the knitting machine during the knitting action. Thehigher the number of stitches per square centimetre, the heavier andthicker the fabric and the lower the air permeability. The inventors,however, have discovered that the risk for glass markings can besubstantially reduced, if not avoided, if the fabric has a higher numberof stitches per surface unit and that this higher number of stitches canbe reached with values of air permeability, thickness and weight whichstill fall within the above-mentioned ranges.

The reduced risk for markings on the glass surface can be explained asfollows:

To reduce the risk on creating marks on the bent glass surface, it isimportant to use a fabric with as much yarn surface as possible on thefabric side which contacts the glass during the bending operation. Thisfor 2 reasons:

1. By having more yarn surface on this contact side, the force to bendthe glass is distributed over more contact surface. The depth to whichextend the fabric might be pressed into the softened glass largelydepends on this force per surface, so less force per unit decreases therisk on having a too large impression of the fabric in the glass, and socreating marks on the glass surface.

2. Because this less force per contact surface unit, the wear due to therepetitive mechanical action on the fabric surface will be reduced. Thismakes the time to have too much yarn pronunciation longer and the riskto have marks will be decreased in time.

The yarns which can be used to realise fabrics, as subject of theinvention are made out of metal fibres, usually stainless steel fibres,possibly blended with glass fibres or ceramic fibres, other hightemperature fibres, such as TWARON®, NOMEX®, meta-aramid fibres,para-aramid fibres, carbon fibres, preox-fibres and other hightemperature resistant man-made fibres. The fibres, of which at least apart being metal fibres, can be intimately blended and possibly plied toa two or more plied yarn or the yarn can be a two- or more plied yarn,where some or all of the single yarns are made out of one fibre type.

At least partially, the yarns will contain metal fibres. Usually, butnot necessarily, stainless steel fibres are used. Alloys such as AISI316 or AISI 316L, AISI 347, or other alloys out of the AISI 300 type areused. Also alloys out of the AISI-400 type or Aluchrome-type alloys canbe used. These fibres can be bundle drawn, as described in patent U.S.Pat. No. 3,379,000, be made by shaving them from a coil, as described inpatent U.S. Pat. No. 4,930,199 or melt extracted. Also metal fibresproduced as described in U.S. Pat. No. 4,220,112 can be used.

These metal fibres have an equivalent diameter usually between 1 and 100μm, and more typically between 6 and 25. The equivalent diameter is thediameter of the circle, which has the same surface as the fibre sectionwhen cut perpendicularly to the axis of the fibres.

Typically, the fabric which is subject of the invention, has an airpermeability of more than 2400 l/10 cm^(2*)h and preferably more than4500l/10 cm²*h. The weight of the fabric will be more than 600 g/m² andless than 2000 g/m². The thickness of the fabric will be not less than0.8 mm and preferably more than 1 mm.

Different knitting structures can be used to provide the fabric assubject of the invention. It was found that knitting structures singlejersey ½, single jersey ⅓ and single jersey {fraction (1/4 )} can beused to provide knitted fabrics, comprising metal fibres with more than90 stitches per square centimetre. Other single jersey structures, withmore floating yarns such as single jersey ⅕, single jersey ⅙ or more,can be used.

By single jersey structures is meant a knitting structure, obtainable byusing one needle bed, providing one stitch for every needle in theneedle bed per row of stitches.

Different gauges can be used to provide the fabric as subject of theinvention. The gauge are the number of needles per inch on the needlebed or beds of the knitting machine. Typically gauges from 10 to 32 canbe used. However it is shown that to obtain more than 90 stitches percm², gauge 16 or more should be used. Best fabrics were provided usinggauge 20 or more, such as gauge 22 or more.

Different yarns with different metrical numbers can be used to providethe fabric as subject of the invention. The metrical number (Nm) of ayarn, as mentioned in the list, is an expression for the fineness of theyarn. It gives you the length of yarn that has a weight of 1 gram. Forreason of comparison, all metrical numbers were recalculated as if allfibres were metal fibres of type AISI 316L. To obtain a fabric assubject of the invention, yarns with metrical number Nm 5.5 can be used.Finer yarns such as Nm 7.5 or Nm 10 could also be used to reach 90 ormore stitches per cm².

Reinforcement multifilament weft yarns with a titre of less than 180tex, such as e.g. metal yarn or glass fiber yarns, can be incorporated,as described in the international application number PCT/BE98/0010.

A fabric as subject of the present invention, with two surfaces having adifferent fibre content can be provided by using the plating techniqueas described in Belgian patent application number 9800212.

According to another aspect of the present invention, there is provideda use of a fabric according to any one of the preceding fabrics forcovering moulds and tempering or press-on rings which are utilised inthe process of forming glass plates, or for covering the means oftransport by which glass plates are moved during the forming process.

Still according to the present invention, there is provided a method forreducing the risk for marking the glass surface during bending.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments of the invention will be explained by making use of nextfigures

FIG. 1 shows a mould on which a separation cloth is mounted.

FIG. 2 shows a side view on a yarn with single yarns which are anintimate blend of different fibres

FIG. 3 shows a side view on a yarn with single yarns which consist outof one type of fibres.

FIG. 4 shows the knitted structure hereafter called “single jersey ½”

FIG. 5 shows the knitted structure hereafter called “single jersey ⅓”

FIG. 6 shows the knitted structure hereafter called “single jersey ¼”

FIG. 7 shows the knitted structure hereafter called “single jersey ⅕”

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

A schematic drawing of a glass shaping mould, covered with separation)is given in FIG. 1. The mould 11 is here covered by a separation cloth12 (shown partially). The glass 14, which is initially pre-shaped butflat, is brought in contact with the mould 11 and the separation cloth12, to transfer the shape of the mould into the glass 14. This can bedone on many different ways. There is always a vacuum created betweenmould 11 and glass 14 when the glass 14 is in contact with the mould 11.Therefore air is sucked through the mould perforations 13 and throughthe separation cloth 12.

It is part of the invention that the yarns, used to provide the knittedfabric as subject of the invention, comprises metal fibres. Metal fibrescan be incorporated in the yarns of the fabric on different ways. It canbe done as shown in FIG. 2, by plying a single yarn, out of 100% metalfibres 15, with other single yarns 16 and 17, e.g. made 100% out of another heat resistant fibre, or a blend out of two or more different heatresistant fibre types. The type of heat resistant fibres used to makethe different single yarns 16 and 17 are not necessarily the same types,and the compositions are not necessarily the same. These single yarns15, 16 and 17 can be multifilament yarns or spun yarns, e.g. rotor- oropen end spun yarn, or ringspun yarn.

An other way of incorporating metal fibres in the yarns is by plyingdifferent single yarns, from which at least on single yarn consists is ablend of metal fibres and at least one non metallic, high temperatureresistant fibre type. This is shown in FIG. 3, where single yarn 18 ismade out of metal fibres 21 and non metallic fibres 22. The other singleyarns 19 and 20 are e.g. made 100% out of other heat resistant fibres,or a blend out of two or more different heat resistant fibre types. Thetype of heat resistant fibres used to make the different single yarns18, 19 and 20 are not necessarily the same types, and the compositionsare not necessarily the same. The single yarns 18, 19 and 20 can bemultifilament yarns or spun yarns, e.g. rotor- or open end spun yarn, orringspun yarn.

Some embodiments of the present invention is given in the tableunderneath, where for different knitted structures, gauge, yarn Nm andknitting structure are given, together with the number of stitches percm², thickness, weight and air permeability. All yarns used for theseexamples are made out of 100% stainless steel fibres, with fibrediameters of 12 μm. The alloy used is AISI 316L.

yarn stitches air permeability thickness weight Embodiment gaugestructure (Nm) (/cm²) (I/10 cm²*h) (mm) (g/m²) embodiment 1 16 singlejersey 1/3 7.5 91 6720 1.00  882 embodiment 2 20 single jersey 1/2 5.594.1 4550 1.25 1010 embodiment 3 20 single jersey 1/2 7.5 100.3 67501.00  741 embodiment 4 20 single jersey 1/3 5.5 101.1 3540 1.5 1192embodiment 5 20 single jersey 1/3 7.5 124.5 4365 1.25  990 embodiment 620 single jersey 1/4 7.5 111.1 4639 1.35 1090 embodiment 7 24 singlejersey 1/2 5.5 96.7 5720 1.05 1016 embodiment 8 24 single jersey 1/2 7.5106.0 8960 0.8  757 embodiment 9 24 single jersey 1/3 5.5 109.3 48361.20 1121 embodiment 10 24 single jersey 1/3 7.5 123.6 5200 1.10  986embodiment 11 24 single jersey 1/3 10 136.6 5800 0.95  826 embodiment 1224 single jersey 1/4 5.5 96.1 3828 1.4 1320 embodiment 13 24 singlejersey 1/4 7.5 114.5 4970 1.3  948

The air permeability is measured conform the international standard ISO9237. Thickness is measured conform ISO 5084 and weight is measuredconform ISO 3801.

The knitting structure is the way how the different stitches are madeout of different yarns.

FIGS. 4 to 7 explains what is meant by the knitting structures singlejersey ½, single jersey ⅓, single jersey ¼ and single jersey ⅕.

FIG. 4 shows the knitting structure using “single jersey ½” 23, whereeach row of stitches 24 is made out of two yarns 26 and 27. The firstyarn 26 makes stitches on every second needle 25 on the needle bed,where the second yarn 27 is only knitted in the same stitch row on theneedles 27 which are not used by yarn 26. As seen in FIG. 5, “singleJersey ⅓” 28 needs three yarns 29, 30 and 31 to make one stitch row,because each yarn makes a stitch on every third needle. FIG. 6 shows“single jersey ¼” 32, where a yarn 33, 34, 35 or 36 is knitted everyfourth needle and so 4 yarns are used to make one row of stitches. Inthe same sense, FIG. 7 shows “single jersey ⅕” 37, where a yarn 38, 39,40, 41 or 42 is knitted every fifth needle and so 5 yarns are used tomake one row of stitches.

What is claimed is:
 1. A knitted fabric, comprising fibers, at leastpart of these fibers being metal fibers, said fabric having 90 or morestitches per square centimeter and having an air permeability higherthan 2400 l/10 cm^(2*) h.
 2. A knitted fabric according to claim 1, saidfabric having 100 or more stitches per square centimeter.
 3. A knittedfabric according to claim 1, having a weight between 600 g/m² and 2000g/m².
 4. A knitted fabric according to claim 1, having a thickness morethan 0.8 mm.
 5. A knitted fabric of claim 1, wherein all of said fibersare metal fibers.
 6. A knitted fabric of claim 1, wherein all of saidfibers are stainless steel fibers.
 7. A knitted fabric of claim 6, inwhich the stainless steel contains at least 16% Cr and 10% Ni.
 8. Aknitted fabric of claim 1, having the single jersey ½ structure.
 9. Aknitted fabric of claim 1, having the single jersey ⅓ structure.
 10. Aknitted fabric of claim 1, having the single jersey ¼ structure.
 11. Amethod of making a knitted fabric comprising utilizing a knittingmachine with gauge equal to or more than 20 to produce a knitted fabricaccording to claim
 1. 12. A method of making a knitted fabric comprisingutilizing a knitting machine with gauge equal to or more than 22 toproduce a knitted fabric according to claim
 1. 13. A knitted fabric ofclaim 1, comprising yarns with metrical number equal to or larger than5.5.
 14. A knitted fabric of claim 1, comprising yarns with metricalnumber equal to or larger than 7.5.
 15. A knitted fabric of claim 1,comprising yarns with metrical number equal to or larger than
 10. 16. Amethod of forming glass plate, comprising covering a mould, a temperingor a press-on ring with a fabric according to claim 1 and forming aglass plate.
 17. A method for reducing the risk for marking on a glassplate during bending of the glass plate, said method comprising thesteps: (a) providing fibers, at least part of these fibers being metalfibers, (b) knitting said fibers into a fabric, such that said fabrichas 90 or more stitches per square centimeter and has an airpermeability higher than 2400 l/10 cm^(2*) h.
 18. A method of formingglass plates, comprising providing a transportation device adapted tomove a glass plate during the forming process, covering thetransportation device with a fabric according to claim 1, and forming aplate.
 19. A knitted fabric according to claim 1, having an airpermeability higher than 4500 l/10 cm^(2*)h.
 20. A knitted fabricaccording to claim 19, having a weight between 600 g/m² and 2000 g/m².21. A glass mould assembly, comprising: a glass mold having a surface;and a knitted fabric covering at least a portion of the surface, whereinthe knitted fabric comprises fibers, at least part of these fibers beingmetal fibers, the fabric having 90 or more stitches per squarecentimeter, and having an air permeability higher than 2400 l/10cm^(2*)h.
 22. A glass mould assembly according to claim 21, wherein thefabric has an air permeability higher than 4500 l/10 cm^(2*)h.
 23. Aglass mould assembly according to claim 22, wherein the fabric has aweight between 600 g/m² and 2000 g/m².
 24. A glass mould assemblyaccording to claim 21, wherein the fabric has more than 110 stitches persquare centimeter.
 25. A glass mould assembly according to claim 24,wherein the fabric has an air permeability higher than 4500 l10cm^(2*)h.
 26. A glass mould assembly according to claim 25, having aweight between 600 g/m² and 2000 g/m².
 27. A glass mould assemblyaccording to claim 21, wherein the knitted fabric further comprisesglass fibers.
 28. A glass mould assembly according to claim 21, whereinthe knitted fabric further comprises ceramic fibers.
 29. A glass mouldassembly according to claim 21, wherein the knitted fabric comprises aplied yarn, wherein the plied yarn comprises a yarn consisting of metalfibers and a yarn comprising one of glass fibers and ceramic fibers. 30.A glass mould assembly according to claim 21, wherein the knitted fabriccomprises a plied yarn, wherein the plied yarn comprises a first yarnconsisting of metal fibers and a second yarn comprising a non-metallicfiber.
 31. A glass mould assembly according to claim 30, wherein theplied yarn comprises a third yarn comprising a fiber different than thefiber of the second yarn.
 32. A glass mould assembly according to claim21, wherein the knitted fabric comprises a plied yarn, wherein the pliedyarn comprises a first yarn comprising a blend of metallic andnon-metallic fibers.
 33. A glass mould assembly according to claim 32,wherein the plied yarn comprises a second yarn comprising a blend ofmetallic and non-metallic fibers.
 34. A glass mould assembly accordingto claim 21, wherein the knitted fabric has two surfaces, and whereinthe two surfaces have a different fiber content.
 35. A glass mouldassembly according to claim 21, said fabric having 100 or more stitchesper square centimeter.
 36. A glass mould assembly according to claim 21,wherein the fabric has a thickness more than 0.8 mm.
 37. A glass mouldassembly according to claim 21, wherein all of said fibers are metalfibers.
 38. A glass mould assembly according to claim 21, wherein all ofsaid fibers are stainless steel fibers.
 39. A glass mould assemblyaccording to claim 21, wherein the fabric has a single jersey ½structure.
 40. A glass mould assembly according to claim 21, wherein thefabric has a single jersey ⅓ structure.
 41. A glass mould assemblyaccording to claim 21, wherein the fabric has a single jersey ¼structure.
 42. A glass mould assembly according to claim 21, wherein thefabric comprises yarns with a metrical number equal to or larger than5.5.
 43. A glass mould assembly according to claim 21, wherein thefabric comprises yarns with a metrical number equal to or larger than7.5.
 44. A glass mould assembly according to claim 21, wherein thefabric comprises yarns with a metrical number equal to or larger than10.
 45. A method of forming glass plates, comprising: providing a glassmold having a surface; and covering at least a portion of the surfacewith a knitted fabric according to claim 1; creating a vacuum behind theknitted fabric and the surface; and placing a piece of glass in contactwith the knitted fabric so that the vacuum draws the piece of glass tothe knitted fabric and the surface.
 46. The method according to claim45, wherein said fabric has 100 or more stitches per square centimeter.47. The method according to claim 45, wherein said fabric has a weightbetween 600 g/m² and 2000 g/m².
 48. The method according to claim 45,wherein said fabric has a thickness of more than 0.8 mm.
 49. The methodaccording to claim 45, wherein all of said fibers are metal fibers. 50.The method according to claim 45, wherein all of said fibers arestainless steel fibers.
 51. The method according to claim 45, whereinthe fabric has a single jersey ½ structure.
 52. The method according toclaim 45, wherein the fabric has a single jersey ⅓ structure.
 53. Themethod according to claim 45, wherein the fabric has a single jersey ¼structure.
 54. The method according to claim 45, wherein the fabriccomprises yarns with a metrical number equal to or larger than 5.5. 55.The method according to claim 45, wherein the fabric comprises yarnswith a metrical number equal to or larger than 7.5.
 56. The methodaccording to claim 45, wherein the fabric comprises yarns with ametrical number equal to or larger than
 10. 57. The method according toclaim 45, further comprising bending the piece of glass around at leasta portion of the curved surface.
 58. The method according to claim 21,wherein the glass mold has a curved surface.